U.S. patent number 7,382,319 [Application Number 10/581,803] was granted by the patent office on 2008-06-03 for antenna structure and communication apparatus including the same.
This patent grant is currently assigned to Murata Manufacturing Co., Ltd.. Invention is credited to Kazunari Kawahata, Junichi Kurita.
United States Patent |
7,382,319 |
Kawahata , et al. |
June 3, 2008 |
Antenna structure and communication apparatus including the
same
Abstract
In an antenna structure including a feeding radiation electrode
and a non-feeding radiation electrode that are electromagnetically
coupled to each other, due to formation of a main slit, the feeding
radiation electrode includes a U-turn portion in the middle of a
path circumventing the main slit from a feeding end to an open end.
A sub-slit for forming an open stub that is connected to the U-turn
portion and that provides the U-turn portion with electrostatic
capacitance is formed in the feeding radiation electrode. By
changing a value of the electrostatic capacitance to be provided by
the open stub to the U-turn portion of the feeding radiation
electrode, variable control of a higher-order resonant frequency F2
of the feeding radiation electrode 2 can be achieved while
suppressing fluctuations in a resonant state (for example, a
fundamental resonant frequency F1 and a Q-value) of a fundamental
resonant frequency band of the feeding radiation electrode, in an
electromagnetic coupling state between the feeding radiation
electrode and the non-feeding radiation electrode, and in an
impedance matching state.
Inventors: |
Kawahata; Kazunari (Machida,
JP), Kurita; Junichi (Fleet, GB) |
Assignee: |
Murata Manufacturing Co., Ltd.
(JP)
|
Family
ID: |
34650035 |
Appl.
No.: |
10/581,803 |
Filed: |
November 30, 2004 |
PCT
Filed: |
November 30, 2004 |
PCT No.: |
PCT/JP2004/017788 |
371(c)(1),(2),(4) Date: |
January 08, 2007 |
PCT
Pub. No.: |
WO2005/055364 |
PCT
Pub. Date: |
June 16, 2005 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20070115177 A1 |
May 24, 2007 |
|
Foreign Application Priority Data
|
|
|
|
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Dec 2, 2003 [JP] |
|
|
2003-402544 |
|
Current U.S.
Class: |
343/700MS;
343/702; 343/770 |
Current CPC
Class: |
H01Q
1/243 (20130101); H01Q 9/0421 (20130101); H01Q
9/0442 (20130101); H01Q 19/005 (20130101); H01Q
5/371 (20150115); H01Q 5/378 (20150115); H01Q
5/385 (20150115); H01Q 5/392 (20150115) |
Current International
Class: |
H01Q
1/38 (20060101); H01Q 1/24 (20060101); H01Q
13/10 (20060101) |
Field of
Search: |
;343/700MS,702,767,770,846,893 |
References Cited
[Referenced By]
U.S. Patent Documents
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6657593 |
December 2003 |
Nagumo et al. |
6950072 |
September 2005 |
Miyata et al. |
|
Foreign Patent Documents
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|
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|
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2-812 |
|
Jan 1990 |
|
JP |
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10-93332 |
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Apr 1998 |
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JP |
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2001-217643 |
|
Aug 2001 |
|
JP |
|
2002-314330 |
|
Oct 2002 |
|
JP |
|
2003-8326 |
|
Jan 2003 |
|
JP |
|
2003-78321 |
|
Mar 2003 |
|
JP |
|
2004-535722 |
|
Nov 2004 |
|
JP |
|
2005-79970 |
|
Mar 2005 |
|
JP |
|
WO 99/03168 |
|
Jan 1999 |
|
WO |
|
WO 01/18909 |
|
Mar 2001 |
|
WO |
|
WO 02/075853 |
|
Sep 2002 |
|
WO |
|
WO 03/007429 |
|
Jan 2003 |
|
WO |
|
Primary Examiner: Chen; Shih-Chao
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb &
Soffen, LLP
Claims
What is claimed is:
1. An antenna structure that comprises a feeding radiation
electrode including one end serving as a feeding end and the other
end serving as an open end and performing an antenna operation in a
plurality of resonant frequency bands and a non-feeding radiation
electrode electromagnetically coupled to the feeding radiation
electrode and performing an antenna operation in a plurality of
resonant frequency bands and said antenna structure being capable
of performing radio communication in at least four resonant
frequency bands, the lowest fundamental resonant frequency band and
a higher-order resonant frequency band higher than the lowest
fundamental resonant frequency band among the plurality of resonant
frequency bands of the feeding radiation electrode, and the lowest
fundamental resonant frequency band and a higher-order resonant
frequency band higher than the lowest fundamental resonant
frequency band among the plurality of resonant frequency bands of
the non-feeding radiation electrode, wherein a main slit is formed
in the feeding radiation electrode by a cut in the feeding
radiation electrode from an electrode edge of the feeding radiation
electrode, wherein one of two sides of the main slit located at an
edge of the feeding radiation electrode that are separated by the
main slit serves as the feeding end and the other side of the two
sides of the main slit located at the edge of the feeding radiation
electrode that are separated by the main slit serves as the open
end, wherein the feeding radiation electrode has a folded shape and
includes a U-turn portion in the middle of a path circumventing the
main slit from the feeding end toward the open end, and wherein a
sub-slit for forming an open stub that is connected to the U-turn
portion and that provides the U-turn portion with electrostatic
capacitance is formed, independent of the main slit, in the feeding
radiation electrode.
2. The antenna structure according to claim 1, wherein the main
slit has a bent shape including a U-shaped portion.
3. The antenna structure according to claim 1, wherein the feeding
radiation electrode is bent in accordance with a virtual extension
line of the sub-slit serving as a bending line.
4. The antenna structure according to claim 1, wherein the feeding
radiation electrode and the non-feeding radiation electrode are
mounted on a dielectric substrate.
5. The antenna structure according to claim 1, wherein an edge of
the feeding end of the feeding radiation electrode, and an edge of
the non-feeding radiation electrode that is adjacent to the edge of
the feeding end of the feeding radiation electrode with a gap
therebetween, serve as short-circuited portions for grounding, and
wherein the distance between outline sides, which face each other,
of the feeding radiation electrode and the non-feeding radiation
electrode that are adjacent to each other increases in a direction
from an end of the outline sides at the short-circuited portion
toward an end of the outline sides opposite to the end at the
short-circuited portion.
6. The antenna structure according to claim 5, wherein at least one
of the feeding radiation electrode and the non-feeding radiation
electrode is one of a plurality of radiation electrodes, and
wherein the feeding radiation electrode and the non-feeding
radiation electrode are aligned in a line such that the
short-circuit portions are aligned on the same side.
7. The antenna structure according to claim 1, wherein an edge of
the feeding end of the feeding radiation electrode, and an edge of
the non-feeding radiation electrode that is adjacent to the edge of
the feeding end of the feeding radiation electrode with a gap
therebetween, serve as short-circuited portions for grounding, and
wherein each of the feeding radiation electrode and the non-feeding
radiation electrode is provided at a shorter side of a rectangular
substrate such that the short-circuited portion is connected to the
shorter side of the substrate.
8. The antenna structure according to claim 7, wherein at least one
of the feeding radiation electrode and the non-feeding radiation
electrode is one of a plurality of radiation electrodes, and
wherein the feeding radiation electrode and the non-feeding
radiation electrode are aligned in a line such that the
short-circuit portions are aligned on the same side.
9. A communication apparatus comprising the antenna structure as
set forth in claim 1, and a high-frequency circuit connected
thereto.
Description
CROSS REFERENCE TO RELATED APPLICATION
The present application is a 35 U.S.C. .sctn.371 national phase
conversion of PCT/JP2004/017788 filed Nov. 30, 2004, which claims
priority of Japanese application no. JP2003-402544 filed Dec. 2,
2003, which are incorporated herein in their entirety.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an antenna structure capable of
performing radio communication in a plurality of different
frequency bands and to a communication apparatus including the
antenna structure.
2. Background Art
FIG. 11a schematically shows an example of an antenna structure
capable of performing radio communication in a plurality of
different frequency bands. An antenna structure 1 includes a
feeding radiation electrode 2 and a non-feeding radiation electrode
3. The feeding radiation electrode 2 is a .lamda./4 radiation
electrode, and is formed by, for example, a conductor plate. A bent
slit 4 including a U-shaped portion is formed in the feeding
radiation electrode 2 by cutting the feeding radiation electrode 2
from an electrode edge. One side Q of the two sides of the slit at
the edge of the feeding radiation electrode that are separated by
the slit 4 serves as a feeding end, and the other side K serves as
an open end. An electrode edge connected to the feeding end Q
serves as a short-circuited portion Gq for grounding. Due to the
formation of the slit 4, the feeding radiation electrode 2 has a
folded shape and includes a U-turn portion T in the middle of the
path from the feeding end Q toward the open end K.
The non-feeding radiation electrode 3 is also formed by a conductor
plate. A bent slit 5 including a U-shaped portion is formed in the
non-feeding radiation electrode 3 by cutting the non-feeding
radiation electrode 3 from an electrode edge. One side Gm of the
two sides at the edge of the non-feeding radiation electrode that
are separated by the slit 5 serves as a short-circuited portion for
grounding, and the other side 6 of the sides at the edge of the
non-feeding radiation electrode serves as an open end. The
non-feeding radiation electrode 3 is disposed adjacent to the
feeding radiation electrode 2 with a gap therebetween such that the
short-circuited portion Gm is adjacent to the short-circuited
portion Gq of the feeding radiation electrode 2 with a gap
therebetween.
For example, as shown by the return loss characteristics in FIG.
11b, a fundamental resonant frequency F1 0f a resonance that mainly
operates due to the feeding radiation electrode 2 is in the
vicinity of a fundamental resonant frequency f1 of a resonance that
mainly operates due to the feeding radiation electrode 2 and the
non-feeding radiation electrode 3 that is electromagnetically
coupled to the feeding radiation electrode 2, and the frequencies
F1 and f1 produce a complex or dual resonance. In addition, a
higher-order resonant frequency F2 of the resonance that mainly
operates due to the feeding radiation electrode 2 is in the
vicinity of a higher-order resonant frequency f2 of the resonance
that mainly operates due to the feeding radiation electrode 2 and
the non-feeding radiation electrode 3 that is electromagnetically
coupled to the feeding radiation electrode 2, and the frequencies
F2 and f2 produce a complex or dual resonance.
The antenna structure 1 shown in FIG. 1 a is capable of performing
radio communication in four resonant frequency bands, that is, a
fundamental resonant frequency band based on the fundamental
resonant frequency F1 and a higher-order resonant frequency band
based on the higher-order resonant frequency F2 of the resonance
that mainly operates due to the feeding radiation electrode 2 and a
fundamental resonant frequency band based on the fundamental
resonant frequency f1 and a higher-order resonant frequency based
on the higher-order resonant frequency f2 of the resonance that
mainly operates due to the feeding radiation electrode 2 and the
non-feeding radiation electrode 3 that is electromagnetically
coupled to the feeding radiation electrode 2.
The antenna structure 1 is installed on, for example, a circuit
substrate of a radio communication apparatus. Thus, the
short-circuited portions Gq and Gm of the feeding radiation
electrode 2 and the non-feeding radiation electrode 3 are connected
to a ground portion of the circuit substrate. In addition, the
feeding end Q of the feeding radiation electrode 2 is connected to,
for example, a high-frequency circuit 8 for radio communication of
the radio communication apparatus.
For example, in the antenna structure 1 shown in FIG. 11a, when a
transmission signal is supplied from the high-frequency circuit 8
of the radio communication apparatus to the feeding end Q of the
feeding radiation electrode 2, the signal supply causes the feeding
radiation electrode 2 to resonate. At the same time, the signal is
also supplied to the non-feeding radiation electrode 3 due to
electromagnetic coupling, and the non-feeding radiation electrode 3
also resonates. Thus, due to the resonance operation (antenna
operation) of the feeding radiation electrode 2 and the non-feeding
radiation electrode 3, a signal is radio-transmitted. In addition,
when the feeding radiation electrode 2 and the non-feeding
radiation electrode 3 resonate (perform an antenna operation) due
to an externally arrived signal (radio wave) and receive the
signal, the received signal is transmitted from the feeding end Q
of the feeding radiation electrode 2 to the high-frequency circuit
8.
Patent Document 1: Japanese Unexamined Patent Application
Publication No. 10-93332
In the structure shown in FIG. 11a, the slit 4 is formed in the
feeding radiation electrode 2. Electrostatic capacitance is
generated in the portion where the slit 4 is formed, and this
electrostatic capacitance (C) and an inductance component (L) of
the feeding radiation electrode 2 form an LC resonant circuit. The
LC resonant circuit is largely involved in a resonant frequency of
the feeding radiation electrode 2. Thus, variable control of the
resonant frequencies F1 and F2 of the feeding radiation electrode 2
can be achieved by changing the position where the slit 4 is
formed, the slit length, and the slit width in order to change a
value of the electrostatic capacitance of the portion where the
slit 4 is formed and a value of the inductance component of the
feeding radiation electrode 2.
However, for example, when the slit length of the slit 4 is
increased in order to lower the higher-order resonant frequency F2
of the feeding radiation electrode 2, the fundamental resonant
frequency F1 of the feeding radiation electrode 2 is also lowered.
Thus, a problem occurs in that it is not possible to lower only the
higher-order resonant frequency F2 to a desired frequency. In other
words, there is a problem in which it is difficult to individually
control the fundamental resonant frequency F1 and the higher-order
resonant frequency F2 of the feeding radiation electrode 2.
In addition, when the slit length of the slit 4 is greatly
increased in order to greatly lower the higher-order resonant
frequency F2 of the feeding radiation electrode 2, the slit 4 may
be formed in a spiral shape (coiled shape), for example, as shown
in FIG. 12. In this case, the inductance component of the feeding
radiation electrode 2 becomes too large, and a signal loss in the
feeding radiation electrode 2 becomes large. Thus, radio wave
(electric field) radiation is suppressed. In addition, a phenomenon
occurs in which electric fields emitted from portions of the
feeding radiation electrode 2 cancel each other. If the slit 4 is
formed in the spiral shape, the antenna gain of the antenna
structure 1 (the feeding radiation electrode 2) is reduced due to
the above-mentioned phenomenon.
SUMMARY OF THE INVENTION
The present invention accordingly provides an improved antenna
structure that is capable of easily performing variable control of
a higher-order resonant frequency of a feeding radiation electrode
while hardly changing a fundamental resonant frequency of the
feeding radiation electrode and avoiding reduction in an antenna
gain, and a communication apparatus including such an antenna
structure.
An antenna structure according to an aspect of the present
invention includes a feeding radiation electrode including one end
serving as a feeding end and the other end serving as an open end
and performing an antenna operation in a plurality of resonant
frequency bands, and a non-feeding radiation electrode
electromagnetically coupled to the feeding radiation electrode and
performing an antenna operation in a plurality of resonant
frequency bands, the antenna structure being capable of performing
radio communication in at least four resonant frequency bands, the
lowest fundamental resonant frequency band and a higher-order
resonant frequency band higher than the lowest fundamental resonant
frequency band among the plurality of resonant frequency bands of
the feeding radiation electrode, and the lowest fundamental
resonant frequency band and a higher-order resonant frequency band
higher than the lowest fundamental resonant frequency band among
the plurality of resonant frequency bands of the non-feeding
radiation electrode. A main slit is formed in the feeding radiation
electrode by cutting the feeding radiation electrode from an
electrode edge of the feeding radiation electrode. One of the two
sides of the main slit at the edge of the feeding radiation
electrode that are separated by the main slit serves as the feeding
end and the other of the two sides of the main slit serves as the
open end. The feeding radiation electrode has a folded shape and
includes a U-turn portion in the middle of a path circumventing the
main slit from the feeding end toward the open end. A sub-slit for
forming an open stub that is connected to the U-turn portion and
that provides the U-turn portion with electrostatic capacitance is
formed, independent of the main slit, in the feeding radiation
electrode. In addition, a communication apparatus according to an
aspect of the present invention includes the antenna structure
having a feature according to the present invention.
According to the aspect of the present invention, the feeding
radiation electrode is a folded-shaped radiation electrode
including a U-turn portion, and an open stub that provides the
U-turn portion with electrostatic capacitance is provided in the
U-turn portion of the folded-shaped feeding radiation electrode.
Due to the formation of the open stub, an LC resonant circuit (tank
circuit) formed by electrostatic capacitance (C) based on the open
stub and an inductance component of the U-turn portion of the
feeding radiation electrode is locally provided in the U-turn
portion of the feeding radiation electrode.
The LC resonant circuit is involved in, or affects a resonant
frequency of the feeding radiation electrode. Due to the difference
between current distribution of a fundamental resonant frequency
and current distribution of a higher-order resonant frequency in
the feeding radiation electrode, the degree of involvement, or
effect of the LC resonant circuit in the higher-order resonant
frequency of the feeding radiation electrode is dramatically larger
than the degree of involvement, or effect of the LC resonant
circuit in the fundamental resonant frequency of the feeding
radiation electrode. Thus, by changing a value of electrostatic
capacitance of the open stub (a value of electrostatic capacitance
to be provided from the open stub to the U-turn portion), the
higher-order resonant frequency of the feeding radiation electrode
can be changed while hardly changing the fundamental resonant
frequency of the feeding radiation electrode.
In addition, instead of changing the higher-order resonant
frequency by changing the shape of the electrode on the current
channel between the feeding end and the open end of the feeding
radiation electrode as in the prior art, the higher-order resonant
frequency is changed by changing a value of electrostatic
capacitance of the open stub. Thus, variable control of the
higher-order resonant frequency of the feeding radiation electrode
can be achieved while considerably avoiding fluctuations in a
resonant state or condition in a resonant frequency band other than
the higher-order resonant frequency band of the feeding radiation
electrode (for example, a resonant frequency, the phase of a
resonance, and a Q-value), an impedance matching state, an
electromagnetic coupling state between the feeding radiation
electrode and the non-feeding radiation electrode, and the
like.
In addition, the open stub is provided by forming the sub-slit in
the feeding radiation electrode. Thus, complication in the shape of
the feeding radiation electrode can be avoided. In addition, the
length (electrical length) of the open stub is changed by changing
the slit length and the cut position of the sub-slit. Thus, a value
of electrostatic capacitance of the open stub can be easily
changed, and variable control of the higher-order resonant
frequency of the feeding radiation electrode can be achieved.
Since miniaturization of the antenna structure is desired, when the
feeding radiation electrode is miniaturized in response to the
desire, the electrical length of the feeding radiation electrode is
reduced. Thus, it is difficult to lower the fundamental resonant
frequency and the higher-order resonant frequency of the feeding
radiation electrode. In contrast, with the present invention, since
the main slit is formed in the feeding radiation electrode, due to
electrostatic capacitance generated in the portion where the main
slit is formed, the fundamental resonant frequency and the
higher-order resonant frequency of the feeding radiation electrode
can be lowered easily. Moreover, since the main slit is bent and
includes a U-shaped portion, the slit length of the main slit is
longer than that of a main slit having a linear shape. Thus, a
value of the electrostatic capacitance of the main slit can be
increased, and an inductance component of the feeding radiation
electrode can be increased. Accordingly, the fundamental resonant
frequency and the higher-order resonant frequency of the feeding
radiation electrode can be much lowered while miniaturizing the
feeding radiation electrode.
In addition, the feeding radiation electrode may be bent in
accordance with a virtual extension line of the sub-slit serving as
a bending line. Thus, advantages described below can be achieved.
For example, when the feeding radiation electrode is disposed on
the circuit substrate such that an electrode face of the feeding
radiation electrode is substantially parallel to the substrate face
of the circuit substrate, by bending the open stub of the feeding
radiation electrode toward the circuit substrate in accordance with
the bending line, which is the virtual extension line of the
sub-slit, to dispose the open stub, for example, in a direction
perpendicular to the circuit substrate, the area of the circuit
substrate occupied by the antenna structure can be reduced. In
other words, miniaturization in the antenna structure can be
achieved.
In addition, since the feeding radiation electrode and the
non-feeding radiation electrode are mounted on a dielectric
substrate, the electrical length of each of the feeding radiation
electrode and the non-feeding radiation electrode can be increased
due to an advantage in shortening of a wavelength by the dielectric
substrate. Thus, compared with a case where the feeding radiation
electrode and the non-feeding radiation electrode are not mounted
on the dielectric substrate, the physical length of the feeding
radiation electrode and the non-feeding radiation electrode to
achieve a desired resonant frequency can be reduced. Thus,
miniaturization of the antenna structure can be advanced.
An edge of the open end of the feeding radiation electrode and an
edge of the non-feeding radiation electrode that is adjacent to the
edge of the feeding end of the feeding radiation electrode with a
gap therebetween both serve as short-circuited portions for
grounding. According to another aspect of the invention, the
distance between outline sides, which face each other, of the
feeding radiation electrode and the non-feeding radiation electrode
that are adjacent to each other may be increased in a direction
from an end of the short-circuited portion of each of the outline
sides to an end opposite to the end of the short-circuited portion.
Thus, an advantage is achieved in which the electromagnetic
coupling state or condition between the feeding radiation electrode
and the non-feeding radiation electrode can be easily controlled.
In other words, it is desirable that the feeding radiation
electrode and the non-feeding radiation electrode be capable of
producing an excellent complex resonance in the electromagnetic
coupling state. In contrast, when the distance between the feeding
radiation electrode and the non-feeding radiation electrode is
reduced in order to miniaturize the antenna structure, mutual
interference between the feeding radiation electrode and the
non-feeding radiation electrode caused by too strong
electromagnetic coupling between the feeding radiation electrode
and the non-feeding radiation electrode may prevent an excellent
complex resonance. Thus, the distance between portions with a
strong electric field (that is, portions away from the
short-circuited portions) of the feeding radiation electrode and
the non-feeding radiation electrode may be increased. Thus, since
the too strong electromagnetic coupling between the feeding
radiation electrode and the non-feeding radiation electrode can be
moderated, an electromagnetic coupling state between the feeding
radiation electrode and the non-feeding radiation electrode
achieving an excellent complex resonance can be easily realized
without increasing the size of the antenna structure.
The feeding radiation electrode and the non-feeding radiation
electrode may be provided at a shorter side of a rectangular
substrate (for example, a circuit substrate) such that the
short-circuited portion is connected to the shorter side of the
substrate. Thus, radio waves attracted from the feeding radiation
electrode and the non-feeding radiation electrode to the circuit
substrate can be suppressed, and radio waves can be easily emitted
from the antenna structure to the outside. Therefore, the antenna
gain of the antenna structure can be improved.
At least one of the feeding radiation electrode and the non-feeding
radiation electrode may be one of a plurality of radiation
electrodes. Thus, the number of resonant frequency bands in which
the antenna structure is capable of performing radio communication
is easily increased.
A communication apparatus including the antenna structure having a
feature according to the present invention is capable of performing
radio communication in a plurality of resonant frequency bands with
an excellent sensitivity without increasing the size of the
communication apparatus.
Other features and advantages of the present invention will become
apparent from the following description of embodiments of invention
which refers to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is an illustration for explaining an antenna structure
according to a first embodiment.
FIG. 1b is an illustration for explaining an example of the
arrangement of a feeding radiation electrode and a non-feeding
radiation electrode shown in FIG. 1a on a substrate.
FIG. 1c is a graph showing an example of the return loss
characteristics of the antenna structure according to the first
embodiment.
FIG. 2 is an illustration for explaining an example of current
distribution and voltage distribution of a radiation electrode.
FIG. 3 is a model diagram showing an antenna structure described in
Patent Document 1.
FIG. 4a is an illustration for explaining another example of a
sub-slit formed in the feeding radiation electrode.
FIG. 4b is an illustration for explaining another example of the
sub-slit formed in the feeding radiation electrode.
FIG. 5 is a model diagram for explaining an antenna structure
according to a second embodiment.
FIG. 6 is a model diagram for explaining an antenna structure
according to a third embodiment.
FIG. 7a is an illustration for explaining an antenna structure
according to a fourth embodiment.
FIG. 7b is a graph showing an example of the return loss
characteristics of the antenna structure according to the fourth
embodiment.
FIG. 8a is a model diagram for explaining an example of the antenna
structure having a feature according to a fifth embodiment.
FIG. 8b is a model diagram for explaining another example of the
antenna structure having a feature according to the fifth
embodiment.
FIG. 8c is a model diagram for explaining another example of the
antenna structure having a feature according to the fifth
embodiment.
FIG. 9 is an illustration for explaining another embodiment.
FIG. 10 is a model diagram showing an example when a sub-slit for
forming an open stub is formed in a non-feeding radiation
electrode.
FIG. 11a is an illustration for explaining an example of a prior
antenna structure.
FIG. 11b is a graph showing an example of the return loss
characteristics of the antenna structure shown in FIG. 11a.
FIG. 12 is a model diagram showing a structural example when a main
slit having a spiral shape (coiled shape) is formed in a feeding
radiation electrode.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Embodiments of the present invention will be described with
reference to the drawings.
FIG. 1a is a perspective view schematically showing an antenna
structure according to a first embodiment. In the explanation of
the first embodiment, the same parts as in the antenna structure
shown in FIG. 11 a are referred to with the same reference numerals
and the descriptions of those same parts will not be repeated
here.
The antenna structure 1 according to the first embodiment includes
the feeding radiation electrode 2 and the non-feeding radiation
electrode 3. For example, as shown by the return loss
characteristics represented by the solid line in FIG. 1c, the
antenna structure 1 is capable of performing radio communication in
four resonant frequency bands, that is, a fundamental resonant
frequency band on a feeding side based on the fundamental resonant
frequency F1 and a higher-order resonant frequency band on the
feeding side based on the higher-order resonant frequency F2 of the
feeding radiation electrode 2 and a fundamental resonant frequency
band on a non-feeding side based on the fundamental resonant
frequency f1 and a higher-order resonant frequency band on the
non-feeding side based on the higher-order resonant frequency f2 of
the non-feeding radiation electrode 3.
In addition, as shown in FIG. 1b, the feeding radiation electrode 2
and the non-feeding radiation electrode 3 are provided, for
example, at an end on a shorter side of a circuit substrate
(rectangular substrate) 9 of a radio communication apparatus such
that the short-circuited portions Gq and Gm are disposed adjacent
to each other and such that the short-circuited portions Gq and Gm
are connected to the shorter side of the substrate.
In the first embodiment, the substantially U-shaped main slit 4 is
formed in the feeding radiation electrode 2. Thus, the feeding
radiation electrode 2 is a folded-shaped radiation electrode
including the U-turn portion T. In addition to the main slit 4, a
sub-slit 10 is formed in the feeding radiation electrode 2.
One side portion and the other side portion of the main slit 4
separated by the main slit 4 have the feeding end Q and the open
end K respectively. The sub-slit 10 is formed by cutting the
feeding radiation electrode 2 from an electrode edge of the open
end K. And the sub-slit 10 extends along an outline side 2.sub.SL
of the feeding radiation electrode 2 in a direction toward the
U-turn portion T of the feeding radiation electrode 2. Due to the
sub-slit 10, an open stub 12 that provides the U-turn portion T
with electrostatic capacitance is formed.
Due to the formation of the open stub 12, an equivalent LC resonant
circuit (tank circuit) is locally formed in the U-turn portion T of
the feeding radiation electrode 2 by electrostatic capacitance (C)
of the open stub 12 and an inductance component (L) of the U-turn
portion T.
FIG. 2 illustrates examples of current distribution and voltage
distribution of the fundamental resonant frequency F1 (fundamental
wave) and current distribution and voltage distribution of the
higher-order resonant frequency F2 (higher-order wave (third
harmonic wave)) in the feeding radiation electrode 2. As is clear
from FIG. 2, the U-turn portion T of the feeding radiation
electrode 2 defines a higher-order-wave maximum current
distribution region and does not define a fundamental-wave maximum
current distribution region. Thus, the LC resonant circuit formed
by the open stub 12 is greatly involved in the higher-order
resonant frequency F2 and has a small influence on the fundamental
resonant frequency F1. Thus, by changing the electrostatic
capacitance to be provided from the open stub 12 to the U-turn
portion T, variable control of the higher-order resonant frequency
F2 can be achieved while hardly changing the fundamental resonant
frequency F1 of the feeding radiation electrode 2.
For example, when the electrostatic capacitance of the open stub 12
is increased by increasing the slit length of the sub-slit 10, the
higher-order resonant frequency F2 on the feeding side can be
lowered to a higher-order resonant frequency F2', as shown by the
wave line cc in FIG. 1c. Moreover, fluctuations in a resonant state
of other resonant frequency bands due to variable control of the
higher-order resonant frequency F2 (for example, a resonant
frequency, a Q-value, and the phase of a resonance), in an
impedance matching state, an electromagnetic coupling state between
the feeding radiation electrode 2 and the non-feeding radiation
electrode 3, can be suppressed.
An example shown by a model diagram of FIG. 3 in which two slits
21a and 21b are formed in a radiation electrode 20 is described in
Patent Document 1. In FIG. 3, reference numeral 22 denotes a
grounding conductor plate for connecting the radiation electrode 20
to the ground, reference numeral 23 denotes a feeding pin for
connecting the radiation electrode 20 to a high-frequency circuit
24, and reference numeral 25 denotes a grounding plate.
In Patent Document 1, the radiation electrode 20 is divided into a
plurality of sections by forming the slits 21a and 21b in the
radiation electrode 20, so that the radiation electrode 20 performs
a plurality of resonances. In other words, the structure described
in Patent Document 1 is equivalent to a state in which a plurality
of radiation electrode parts 20A, 20B, and 20C is connected to the
common feeding pin 23 (and to the high-frequency circuit 24). That
is, the slits 21a and 21b are provided for forming the plurality of
radiation electrode parts 20A, 20B, and 20C and for causing the
radiation electrode 20 to perform a plurality of resonances.
In contrast, in the structure of the first embodiment, the main
slit 4 of the feeding radiation electrode 2 is provided for
controlling the fundamental resonant frequency F1 and the
higher-order resonant frequency F2 of the feeding radiation
electrode 2, and the sub-slit 10 is provided for forming the open
stub 12 that provides the U-turn portion T of the feeding radiation
electrode 2 with electrostatic capacitance. As described above, the
main slit 4 and the sub-slit 10 shown in the first embodiment have
functions different from the slits 21a and 21b of the radiation
electrode 20 described in Patent Document 1. The structure of the
first embodiment in which the main slit 4 for controlling resonant
frequencies and the sub-slit 10 for forming an open stub are formed
in the feeding radiation electrode 2 is innovative.
In the example shown in FIG. 1a, the sub-slit 10 has a linear
shape. However, the shape of the sub-slit 10 is not particularly
limited as long as the sub-slit 10 is capable of forming the open
stub 12 that provides the U-turn portion T of the feeding radiation
electrode 2 with electrostatic capacitance. For example, in order
to increase the slit length of the sub-slit 10 to lower the
higher-order resonant frequency F2 of the feeding radiation
electrode 2, the sub-slit 10 may be formed along the outline side
2.sub.SL of the feeding radiation electrode 2 by cutting the
feeding radiation electrode 2 from an electrode edge of the open
end K and then cutting toward the U-turn portion T, as shown in
FIG. 4a.
In addition, in order to increase the slit length of the sub-slit
10 to be longer than the slit length in the example shown in FIG.
1a or FIG. 4a, for example, the sub-slit 10 may have a shape shown
in FIG. 4b. The sub-slit 10 shown in FIG. 4b has an L shape and is
formed by branching from the main slit 4 on the electrode cut side
of the main slit 4 and extending along outline sides 2.sub.FR and
2.sub.SL of the feeding radiation electrode 2.
A second embodiment is described next. In the explanation of the
second embodiment, the same parts as in the first embodiment are
referred to with the same reference numerals and the descriptions
of those same parts will not be repeated here.
In the second embodiment, as shown by a model diagram of FIG. 5,
the feeding radiation electrode 2 has a shape in which the open
stub 12 is bent toward the circuit substrate 9 in accordance with a
virtual extension line .beta. of the sub-slit 10 shown by a dotted
line in FIG. 5.
In the second embodiment, since the open stub 12 is a portion that
is not involved in radio wave radiation, the open stub 12 can be
bent without considering deterioration of a radio wave radiation
state. Due to bending of the open stub 12, the area of the circuit
substrate 9 occupied by the antenna structure 1 (the feeding
radiation electrode 2) can be reduced (that is, the antenna
structure 1 can be miniaturized). The other structural features are
similar to those in the first embodiment, and advantages similar to
those of the first embodiment can be achieved.
A third embodiment is described next. In the explanation of the
third embodiment, the same parts as in the first and second
embodiments are referred to with the same reference numerals and
the descriptions of those same parts will not be repeated here.
In the third embodiment, as shown in FIG. 6, the distance D between
outline sides 2.sub.SR and 3.sub.SL, which face each other, of the
feeding radiation electrode 2 and the non-feeding radiation
electrode 3 that are adjacent to each other increases in a
direction from the short-circuited portions Gq and Gm of the
outline sides 2.sub.SR and 3.sub.SL toward an end E opposite to the
short-circuited portions Gq and Gm.
The other structural features are similar to those in the first and
second embodiments. In the example shown in FIG. 6, an example when
the structure of the third embodiment is applied to the structure
shown in the first embodiment is illustrated. However, the
structure of the third embodiment may also be applied, for example,
to the antenna structure 1 shown in the second embodiment in which
the open stub 12 is bent.
Advantages similar to those in the first and second embodiments can
be achieved in the third embodiment. In addition, the third
embodiment achieves an advantage in that an electromagnetic
coupling state between the feeding radiation electrode 2 and the
non-feeding radiation electrode 3 can be controlled easily and in
that an excellent complex resonance of the feeding radiation
electrode 2 and the non-feeding radiation electrode 3 can be easily
achieved.
A fourth embodiment is described next. In the explanation of the
fourth embodiment, the same parts as in the first to third
embodiments are referred to with the same reference numerals and
the descriptions of those same parts will not be repeated here.
In the fourth embodiment, as shown in FIG. 7a, in addition to the
feeding radiation electrode 2 and the non-feeding radiation
electrode 3, a non-feeding radiation electrode 14 is provided. The
non-feeding radiation electrode 14 is electromagnetically coupled
to the feeding radiation electrode 2 via the non-feeding radiation
electrode 3. The non-feeding radiation electrode 14 includes a
short-circuited portion Gn for grounding. The feeding radiation
electrode 2, the non-feeding radiation electrode 3, and the
non-feeding radiation electrode 14 are aligned in a line such that
the short-circuited portions Gq, Gm, and Gn are aligned with
respect to each other.
As shown by the return loss characteristics in FIG. 7b, the antenna
structure 1 according to the fourth embodiment is capable of
including, in addition to four resonant frequency bands based on
the feeding radiation electrode 2 and the non-feeding radiation
electrode 3, another resonant frequency band based on a resonant
frequency fa of the non-feeding radiation electrode 14.
Structural features of the fourth embodiment other than the
structural feature relating to the non-feeding radiation electrode
14 are similar to those in the first to third embodiments. In the
example shown in FIG. 7a, the feeding radiation electrode 2 and the
non-feeding radiation electrode 3 have structures as in the first
embodiment. However, the feeding radiation electrode 2 and the
non-feeding radiation electrode 3 may have the structure as in the
second or third embodiment, for example.
A fifth embodiment is described next. In the fifth embodiment, the
same parts as in the first to fourth embodiments are referred to
with the same reference numerals and the descriptions of those same
parts will not be repeated here.
In the fifth embodiment, as shown in FIGS. 8a, 8b, and 8c, the
feeding radiation electrode 2 and the non-feeding radiation
electrode 3 described in the first, second, or third embodiment and
optionally the non-feeding radiation electrode 14 described in the
fourth embodiment are mounted on a dielectric substrate 15 made of,
for example, dielectric ceramics or a compound dielectric material.
The other structural features are similar to those in the first to
fourth embodiments.
In the fifth embodiment, since the feeding radiation electrode 2
and the non-feeding radiation electrodes 3 and optionally 14 are
mounted on the dielectric substrate 15, due to an advantage in
shortening of a wavelength by dielectric medium, the electrical
length of each of the feeding radiation electrode 2, the
non-feeding radiation electrode 3, and the non-feeding radiation
electrode 14 can be increased. Thus, the radiation electrodes 2, 3,
and 14 can be miniaturized. In other words, miniaturization of the
antenna structure 1 can be easily achieved.
A sixth embodiment is described next. The sixth embodiment relates
to a communication apparatus. The communication apparatus according
to the sixth embodiment includes the antenna structure 1 described
in the first, second, third, fourth, or fifth embodiment. Since the
antenna structure 1 has been described above, the description of
the antenna structure 1 will be omitted. In addition, apart from
the antenna structure 1, various structures may be adopted for the
communication apparatus. Any structure can be adopted, such as the
high frequency circuit 8, and the description of the structure of
the communication apparatus is omitted here.
The present invention is not limited to each of the first to sixth
embodiments, and various modifications can be made to the present
invention. For example, in the fifth embodiment, the feeding
radiation electrode 2 and the non-feeding radiation electrodes 3
and 14 are formed by conductor plates, as in each of the first to
fourth embodiments. However, the feeding radiation electrode 2 and
the non-feeding radiation electrodes 3 and 14 may be formed by
conductor films produced on an outer surface of the dielectric
substrate 15 by a film deposition technology, such as sputtering,
vapor deposition, or printing.
In addition, for the return loss characteristics shown in FIG. 1c
or FIG. 7b, an example in which a fundamental resonant frequency
band of the feeding radiation electrode 2 and a fundamental
resonance frequency band of the non-feeding radiation electrode 3
produce a complex resonance and the width of the fundamental
resonant frequency bands is increased is described. However, for
example, when each of the fundamental resonant frequency bands of
the feeding radiation electrode 2 and the non-feeding radiation
electrode 3 has a bandwidth in which radio communication can be
performed satisfactorily only in the individual fundamental
resonant frequency band, the fundamental resonance frequency band
of the feeding radiation electrode 2 and the fundamental resonant
frequency band of the non-feeding radiation electrode 3 may be
independent of each other, for example, as shown by the return loss
characteristics in FIG. 9, instead of producing a complex resonance
by the fundamental resonant frequency band of the feeding radiation
electrode 2 and the fundamental resonant frequency band of the
non-feeding radiation electrode 3.
In addition, in the fourth embodiment, the non-feeding radiation
electrode 14 is provided, in addition to the feeding radiation
electrode 2 and the non-feeding radiation electrode 3. However, in
addition to the feeding radiation electrode 2 and the non-feeding
radiation electrode 3, two or more non-feeding radiation electrodes
may be provided. Alternatively, in addition to the feeding
radiation electrode 2 and the non-feeding radiation electrode 3,
one or more feeding radiation electrodes may be provided, instead
of providing another non-feeding radiation electrode.
Alternatively, a plurality of feeding radiation electrodes and a
plurality of non-feeding radiation electrodes including the feeding
radiation electrode 2 and the non-feeding radiation electrode 3
described in any of the first to fifth embodiments may be provided.
When three or more radiation electrodes are provided as described
above, such radiation electrodes are aligned in a line such that
short-circuited portions are aligned on the same side.
In addition, the open stub 12 is provided by forming the sub-slit
10 in the feeding radiation electrode 2 in each of the first to
sixth embodiments. However, for example, as shown by a model
diagram in FIG. 10, in addition to the feeding radiation electrode
2, the non-feeding radiation electrode 3 is provided with an open
stub 16 that provides the U-turn portion of the non-feeding
radiation electrode 3 with electrostatic capacitance by forming a
sub-slit 17, which is similar to the sub-slit 10 of the feeding
radiation electrode 2 described in each of the first to fifth
embodiments, for forming the open stub.
In this case, variable control of the higher-order resonant
frequency f2 of the non-feeding radiation electrode 3, as well as
the higher-order resonant frequency F2 of the feeding radiation
electrode 2, can be performed easily. Although a structural example
in which the sub-slit 17 for forming an open stub is formed in the
non-feeding radiation electrode 3 of the antenna structure 1
described in the first embodiment is shown in FIG. 10, in addition,
the sub-slit 17 for forming an open stub may be formed in the
non-feeding radiation electrode 3 of the antenna structure 1
according to each of the second to fifth embodiments. In addition,
the non-feeding radiation electrode 3 may include the open stub 16
that is bent in accordance with a virtual extension line of the
sub-slit 17 serving as a bending line.
Since a structure easily achieving excellent radio communication in
a plurality of required frequency bands is provided, the present
invention is effective for, for example, an antenna structure and a
communication apparatus used for a plurality of radio communication
systems in common.
Although the present invention has been described in relation to
particular embodiments thereof, many other variations and
modifications and other uses will become apparent to those skilled
in the art. Therefore, the present invention is not limited by the
specific disclosure herein.
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